Single differential cross-sections for transfer-loss (TL) leading to the production of
O5+(1s2s 3S)nl 4L states were computed for 0.2 - 1.2 MeV/u
collisions of O5+(1s22s) ions with He
and H2 targets. At these collision energies, 1s loss is significant and electron transfer
to n = 3 - 4
levels is dominant. Furthermore, due to spin conservation, quartet states can only be populated by
TL. Within the independent particle model, the probability of 1s electron loss from O5+(1s22s)
projectiles was calculated using the semi-classical approach, while the probability for electron transfer
to the O5+(1s2s 3S)nl 4L states (n>=2) was computed using the continuum distorted wave (CDW)
approximation. The majority of states with n > 2, can be assumed to have su±cient time to even-
tually decay with an almost 100% probability to the long-living metastable 1s2s2p 4P level via a
much faster sequence of electric dipole transitions, thus establishing an upper limit to such cascade
contributions. The inclusion of this cascade feeding is found to lead to a strong enhancement in
the production of the 1s2s2p 4P states, particularly for collisions with the H2 target, thus reducing
dramatically the existing two-order of magnitude discrepancy between older TL calculations (for
n = 2 only) and existing zero-degree Auger projectile electron spectroscopy measurements.

This work was supported by the
Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences,
Office of Science,
U.S. Department of Energy.